Do we need quantum computers

We are constantly told how wonderful quantum computers will be and a great deal of effort seems to be put into building them with about as much success as nuclear fusion (hot and cold) and that they will revolutionise cryptography.Is not sufficiently secure cryptography already available is it such a problem.

I don't know how much help they'll be for most computing tasks, but for certain ones like finding out which two prime numbers are the factors of an encryption key they will enable instant cracking of internet communications which are supposed to be private, so it may cause a lot of problems when you're trying to buy things online. For that reason, it may initially cause more problems than it solves. There is actually a more limited kind of quantum computer available today, and you can read about it here: http://forum.osdev.org/viewtopic.php?f=11&t=24617&start=0 [Links inactive - To make links active and clickable, login or click here to register]. If you've got $10,000,000 spare, you can even buy one.

It would seem that they are about as useful as nuclear bombs are as long as you are the only power that has them, OK you can pry into other nations secure communications but if others have them it makes secure communication difficult for everyone.I think there is no chance of criminals using them to get into bank accounts etc (I might have said the same thing about regular computers in the forties) as they are far too difficult to construct and operate and there are much easier ways.

The thing is that quantum cryptography is already available, so if someone develops a quantum computer and renders current cryptography obsolete, we already know how to build an alternative that is much more resistant to cracking. (Rolling it out worldwide will take time, of course.)

Quantum Computing is valuable in the many tasks that require extensive parallelism. This is not just codebreaking. This class of problem occurs frequently in modelling complex systems (the weather, the economy, multi-body dynamics etc.). It is not discussed much by experts in the individual fields because it is, as yet, impractical.

Most computers operate on binary bits which are supposed to be in one of two possible states.

Quantum computers operate on Q-bits which are in all possible states at the same time. If you have a large range of possible input values, a conventional computer has to laboriously input each possible value in series. A quantum computer inputs them all simultaneously which is obviously a useful time saving technique, if you can actually get it all to work!

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Most computers operate on binary bits which are supposed to be in one of two possible states.

Quantum computers operate on Q-bits which are in all possible states at the same time. If you have a large range of possible input values, a conventional computer has to laboriously input each possible value in series. A quantum computer inputs them all simultaneously which is obviously a useful time saving technique, if you can actually get it all to work!

I cannot see how you won't get a perfectly correct answer - but you won't know which of the myriad questions you could possibly have asked it will be the perfectly correct answer to!

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Scott Aaronson recently wrote a http://www.scottaaronson.com/blog/?p=902 [Links inactive - To make links active and clickable, login or click here to register] about the possibility of Quantum Computing - he gives a nice explanation http://spectrum.ieee.org/tech-talk/computing/hardware/why-im-wagering-100000-on-quantum-computing [Links inactive - To make links active and clickable, login or click here to register].

It is on the difference between something being really really hard (which he believes QC is) and impossible (which he has challenged people to prove)

H/t to ajb - and BTW his blog is a great read on QC and complexity in general

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There’s no sense in being precise when you don’t even know what you’re talking about. John Von Neumann

At the surface, we may appear as intellects, helpful people, friendly staff or protectors of the interwebs. Deep down inside, we're all trolls. CaptainPanic @ sf.n